1. Field of the Invention
The present invention relates to an engine configured to drive a diaphragm fuel pump using the pressure fluctuation in a crank chamber of the engine.
2. Description of the Related Art
Recently, due to increasing public awareness regarding environmental issues, enhancement of emission control and so forth, a two-stroke engine has been taken over by a four-stroke engine, as a drive engine for a working machine such as a brush cutter, a chain saw and a backpack blower being carried by the user's hand or carried on the user's shoulder.
Some two-stroke engines use the pressure fluctuation in an intake port as a power source to drive a fuel pump (diaphragm fuel pump) as disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2005-140027 (Patent literature 1) and Japanese Patent Application Laid-Open Publication No. HEI9-158806 (Patent literature 2). However, most two-stroke engines use the pressure fluctuation in a crank chamber. In this case, a positive pressure and a negative pressure generated in the crank chamber are often used as a power source to drive a diaphragm chamber in a diaphragm fuel pump, as disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 11E13-189363 (Patent literature 3), Japanese Patent Application Laid-Open Publication No. 2003-172221 (Patent literature 4) and Japanese Patent Application Laid-Open Publication No. 2001-207914 (Patent literature 5).
In the cases of Patent literature 1 and patent literature 2, that is, if a diaphragm fuel pump in a four-stroke engine is driven by using the pressure fluctuation in an intake port as a power source, there is a problem that the diaphragm fuel pump cannot acquire sufficient power because the pressure in the intake port changes only once while a crankshaft rotates twice. In addition, in the cases of Patent literature 3, Patent literature 4 and Patent literature 5, that is, if a diaphragm fuel pump is driven by using the pressure fluctuation in a crank chamber, it is possible to acquire power by which the pressure changes once while a crankshaft rotates once, and consequently solve the above-described problem. However, a positive pressure in the crank chamber affects the inside of a diaphragm chamber, and therefore the oil from the crank chamber enters the diaphragm chamber and a path in communication with the diaphragm chamber. As a result, the pressure fluctuation cannot be transferred to the diaphragm chamber, and this may cause eventually the diaphragm fuel pump failure.